Applying this analogy to comments in online discussion forums, Medvedev et al. defined a root node as a social media post, and `immigrants' as top-level comments, which can each have reply-comment `offspring' [1]}. The example in Fig. REF  illustrates a small discussion cascade. The Hawkes process is particularly well-suited to the modelling of discussion threads, and has been previously used to predict the final retweet cascade size and shape [2]}, [3]} based on user history [4]}, circadian rhythms [5]}, or other user properties [6]}.
